High initial permeability fe-48ni product and process for manufacturing same

ABSTRACT

A process is described for producing iron-nickel magnetic alloys having a high initial permeability. Various steps including air melting, vacuum remelting with critical control of the carbon oxygen and sulfur levels are employed along with the secondary recrystallized microstructure to achieve the desired results.

[lite States Patent Coiling [54] HIGH INITIAL PERMEABUJITY FE-48NI PRODUCT AND PROCESS FOR MANUFACTURING SAME [72] Inventor: David A. Colling, Murrysville, Pa.

[73] Assignee: Westinghouse Electric Corporation, Pittsburgh, Pa.

[22] Filed: July 28,1969

[21] Appl.No.: 845,134

[52] US. Cl ..148/120, 75/170,148/2,

1,807,021 5/1931 Yenson ..14s/12 2x 2,558,104 6/1951 Scharschu ..148/2 X 2,569,468 10/1951 Gaugler 148/122 X 2,815,279 12/1957 Moore et al... ..75/49 X 3,235,373 2/1966 Poole et al ..75/10 3,247,031 4/1966 Littmann et al. ..148/120 3,297,434 l/1967 Littmann et al ..148/121 X 3,553,035 1/1971 Coiling et a1 ..148/120 Primary Examiner-L. Dewayne Rutledge Assistant Examiner-G. K. White Attorney-F. Shapoe and R. T. Randig [57] ABSTRACT A process is described for producing iron-nickel magnetic a1- loys having a high initial permeability. Various steps including air melting, vacuum remelting with critical control of the carbon oxygen and sulfur levels are employed along with the secondary recrystallized microstructure to achieve the desired results.

7 Claims, 2 Drawing Figures PATENTEB APR 18 m2 Vacuum Arc Remelt m w o E: @82 5&3

Carbon Content, ppm

FIG.

I0 I 5 I w m I l p a w m m m A A 2 I C C 3% G m m C H H n l l e W m I N 0 l 1 r 0 0 0 0 m m m .5 m

IIIGII INITIAL PERMEABILITY FIE-48M PRODUCT AND PROCESS FOR MANUFACTURING SAME CROSS REFERENCE TO RELATED APPLICATION BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing magnetic material which is useful for shielding purposes and for various other component-parts where a high initial permeability is needed, said high initial permeability being taken as a measure of the permeability at an induction of 40 gausses.

2. Description of the Prior Art The alloy of iron in which about 48% by weight of nickel is present has been known for some time and has been utilized in magnetic shielding applications. Of particular interest is the fact that when properly processed, the iron-nickel alloy has the ability to exhibit a high initial permeability which makes the material eminently suited for shielding applications. In producing such iron-nickel alloys induction melting has been preferred because of the success in obtaining high purity products. During such induction melting carbon deoxidation has been employed in order to reduce the oxygen content of the material without introducing undesirable components within the melt. Accordingly, sufficiently high amounts of carbon were charged into the melt in order to reduce the oxygen content to a desired low level.

It has been found however that high amounts of residual carbon were always present within the material as a result of such carbon deoxidation and said carbon of necessity had to be removed during a final decarburization anneal in order to prevent the phenomenon known as aging from occurring to the material, said aging resulting in significantly inferior magnetic characteristics within the metal.

SUMMARY OF THE INVENTION The process of the present invention is directed to a method for producing iron-48% nickel magnetic alloys which are characterized by having a high initial penneability. To produce the alloy, suitable components are selected and air melted wherein the carbon, oxygen and sulfur contents are critically controlled within a given range. Thereafter the air melted heat is teemed into an ingot and at the same time the carbon content is adjusted to produce a critical carbon content range. Thereafter the resulting ingot is employed as an electrode and the material is vacuum remelted by consumable arc techniques thereby critically controlling the carbon and oxygen, and to some extent, the sulfur content of the material. Following the vacuum remelting the resulting ingot may be forged and hot-rolled followed by cold rolling to finish gauge without any intermediate heat treatment. Upon final annealing at the desired temperature range a coarse secondary recrystallized microstructure is obtained thereby resulting in the alloy exhibiting a high initial permeability of at least about 10,000 gauss when measured at an induction of 40 gauss at 60 Hz.

It is an object of the present invention to provide a process for producing iron-nickel magnetic alloys exhibiting high initial permeabilities.

Another object of the present invention is to provide a method for controlling the initial permeability of iron-nickel allo s.

A more specific object of the present invention is to provide a process whereby critically controlling in the chemistry of an iron-nickel alloy a predetermined initial permeability may be developed within the alloy.

DESCRIPTION OF THE DRAWINGS Other objects of the present invention will become apparent when read in conjunction with the following description and the drawings in which:

FIG. I is a graph of the carbon-oxygen relationship for both air melted and vacuum arc remelted Fe-48Ni alloys; and

FIG. 2 is a graph illustrating the efiect of oxygen on the initial permeability of an iron-nickel alloy when subjected to a final anneal at a temperature at l, 1 50 C. and l,200 C.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention relates to a method for producing an alloy of iron containing nominally about 48% nickel which alloy is highly useful where high permeabilities at low inductions are required. More specifically, the alloy to which the method of the present invention relates contains between about 47 and about 50% by weight of nickel, about 0.60% to about 1.0% manganese, less than 0.005% sulfur, with carbon and oxygen being at low levels, the oxygen being less than 5 ppm, and the balance being essentially iron with incidental impurities.

While it will be noted from the data set forth hereinafter that it is desirable to maintain the sulfur content at less than about 0.005%, since it is the final sulfur content which is one critical controlling factor insofar as the final magnetic characteristics are concerned, in practice this final sulfur content is preferably maintained at a value of less than about two parts per million. While the carbon content of the initially air melted material may range in amount of up to about 0.03 5% maximum, nonetheless, after the final annealing wherein decarburization and the desulfurization take place, the desired final carbon content is considerably lower than the initial air melt or the vacuum remelt analysis as will be set forth more fully hereinafter.

The furnace, preferably an air induction furnace, is charged with suitable alloying components having the desired degree of purity and in this respect it should be noted that it is desirable to maintain the impurity content at the absolute minimum commensurate with good economic fumace practice. The alloying components are preferably air melted in an induction furnace since good control of the impurity content can be achieved. While the initial amount of carbon which is charged into the melt may be high, that is, aiming at a value of between about 0.10 and about 0.15% carbon, nonetheless the deoxidation produced by the carbon reacting with the oxygen results in the carbon level being reduced in some instances to below a value of about 0.015%.

Referring now to the air melt curve in FIG. 1 of the drawings, which curves were produced from work on this invention, it can be seen that a critical relationship exists in the air melt in order to have sufficient deoxidation of the final alloy product. Thus it will be seen that if the carbon content is below about 0.015% in the air melt a high oxygen content necessarily results in the air melt. As seen from the vacuum arc remelt curve in FIG. 1, upon vacuum arc remelting the alloy when the carbon content is low, insufiicient deoxidation results and this detrimentally affects the magnetic characteristics as will be shown later. Consequently, it is preferred during air melting to achieve a high degree of deoxidation by having sufficient carbon present and thereafter adding additional carbon if necessary, during the teeming thereof so that during subsequent vacuum remelting there is sufficient carbon whereby the final desirable carbon and low oxygen content relationship can be obtained as is set forth in FIG. 1.

From FIG. 1 it is seen that where the initial air melt chemistry with respect to the carbon content is maintained within the range between about 0.020 and about 0.035% carbon (200 to 350 ppm), the vacuum arc remelting of this alloy will result in a further reduction in oxygen to a final low oxygen content as indicated by the lower curve. To obtain the desired initial permeability in the processed material it is desired that oxygen be less than 5 ppm in the final product. Thus from the relationship of the curves in FIG. 1 the predetermined low oxygen content can be obtained and from FIG. 2 the desired final magnetic characteristic can be obtained by carefully controlling the chemistry of both the air melt material and the subsequently vacuum arc remelted and processed material.

After the melt has been subjected to an initial carbon deoxidation and the proper chemistry is obtained between the nickel, iron and manganese content, it is desirable to teem the air melted components into an ingot form while at the same time adjusting the carbon content to produce a carbon content within the range between about 0.020 and about 0.035%. This is usually accomplished by adding about 29g times the necessary carbon additions with respect to that desired to produce a carbon content within the range above specified.

Following the casting of the air melt into an ingot form, the ingot is thereafter utilized as an electrode and consumably remelted while being subjected to a vacuum of better than about microns. Consumable arc melting or electron beam melting can be applied to the ingot electrode. Thus it can be seen from FIG. 1 that where the carbon content in the electrode has been adjusted to a value of between about 0.020 and about 0.035% by weight the vacuum remelting results in a large reduction in the oxygen content so that the oxygen present within the vacuum remelted heat will be reduced to a value of about five parts per million maximum.

The vacuum remelted ingot may thereafter be hot worked in any desirable manner. It has been found convenient in large commercial tonnages to initially forge the vacuum remelted ingot until a desired slab size is obtained and thereafter the slab may be reheated and hot rolled to any desired intermediate thickness usually within the range between about 0.100 and about 0.250 inch in thickness. The hot-rolled band is thereafter descaled either mechanically or chemically and without any intermediate heat treatment, the hot-rolled band is cold-rolled to the finish gauge usually of the order of less than about 0.018 inch in thickness. The finish gauge material is thereafter subjected to a final annealing heat treatment in the presence of a protective atmosphere in order to reduce the carbon and the sulfur contents to the desired low levels and to provide the alloy with a coarse grained secondary recrystallized microstructure. The final annealing takes place at a temalloy at a temperature of about 1,150 C since most commercial annealing furnaces in the industry have an upper economical operating limit of 1,150 C. Not only would it require new annealing equipment to anneal at l,200 C., but operating costs, percent of scrap and other problems are greatly increased at l,200 C. as compared to 1,150 C. annealing. To anneal at l,250 C. would increase these costs and difficulties even more. Where the application can bear the higher costs to secure the improved results secured by annealing at 1,200 to l,250 C., these anneals can be employed.

Referring now to FIG. 2 of the drawings, the effect of the final oxygen content on the initial permeability of the alloys processed to final gauge in accordance with the method of the present invention is clearly set forth. Where the oxygen content is reduced to the desired level of less than about five parts per million, a sulfur content of less than about two parts per million and the alloy is annealed at a temperature of 1,I C. a consistently high initial permeability of about 10,000 gauss and higher at an induction of 40 gauss at Hz can be obtained, while annealing at l,200 C., an initial permeability of about 14,000 to 15,000 is obtained when measured at an induction of 40 gauss at 60 Hz. At the lower annealing temperatures for example, at 1,150 C., the initial permeability is believed to be lower because of the lesser degree of removal of the sulfur as will be fully set forth hereinafter. On the other hand, regardless of the sulfur content, where higher amounts of oxygen are retained within the final material and the material is subjected to a l,200 C. anneal it will be seen that an oxygen content of substantially over 8 ppm result in a reduction of the initial permeability from a value of about 15,000 to a value of about 12,000. The effect of sulfur may be observed by comparing the curves of FIG. 2 wherein the lower temperature annealing heat treatment is consistently below the higher annealing temperature at which more sulfur is removed.

In order to more clearly demonstrate the method of the present invention reference may be had to the following specific examples of five heats which were made and tested employing the process of the present invention. Reference is directed to Table 1 which tabulates the melt calculation used on each of the heats made and treated in accordance with the process of the present invention.

TABLE I Element addition to charge Percent Wt. (1b.) Ni Fe Mn 8 C 47. 60 2, 493. 75 2, 493. 75 .90 47.25 47.25 .14 7. 35 7. 35 A-101 Fe, Lot No. 25053 Glass, 1.5# 51. 46 2, 701. 2,701.40 .14 11 Totals 100. 00 5, 250.09 2, 493. 2, 791. 40 47. 25

perature within the range between about 1,150 and about l,250 C while employing a hydrogen atmosphere having a dew point of preferably less than about 40 C. The heat treatment is preferably maintained for a period of between about 2 and about 16 hours with optimum results being obtained after about 4 hours at a temperature of about l,200 C. using hydrogen with a dew point of about 75 C. The anneal should substantially completely secondarily recrystallize the alloy into coarse grains, such that a major portion of the volume comprises grains of an average diameter of 0.25 inch or greater. It is desired to be able to secondarily recrystallize the The raw materials were charged into an induction furnace in which a wash heat had been melted previously containing substantially the same charge calculation. Various power settings were used with each heat resulting in variations in the total heat time. In each heat a carbon check analysis was made and based thereon specific carbon additions were made to three of the five heats so as to obtain the final carbon content within the desired range. Reference is directed to Table II which lists the heat numbers and the carbon control that was exercised in air melting the materials in an induction furnace and the actual aim air melt chemistry.

TABLE II Air melt ingots (Weight percent except where noted) Total Percent heat Nominal Analysis 0 added time carbon in carbon Carbon Final that Is Heat No (mins.) charge check added carbon retained Fe NI Mn (p.p.m.) S HK3575 158 0.14 015 010 .019 40 Bal- 47. 67 71 197 .002 HK3570 172 0. 14 010 015 016 40 BaL 47. 86 68 233 002 HK3577 0.14 .035 .034 BB1." 47.94 .76 83 .004 H K3578 146 0.14 .030 .030 Ba1 47. 76 .75 76 008 HK3579 0.14 .011 .015 .018 47 Ba1 47.90 .74 201 .003

From Table II it will be noted that while each of the heats were charged to have a carbon content of about 0.14 the carbon deoxidation which has occurred during air melting has resulted in the carbon content being significantly reduced, in

ture that the effect of the vacuum arc remelting of the metals is effective for reducing the sulfur content moderately although final sulfur removal to the requisite low level only occurs during final heat treatment. During said melting the some cases to values of about 0.010%. Since it is desired to av rag pr ssur th t furnace, as measured on a Stokes marntam the air melt chemistry with a carbon content within Gauge, was less than about micronsthe range between about 0.021 and about 0,035% carbon Each of the five heats which were vacuum arc remelted prior to vacuum remelting, carbon was added to the he t d were thereafter forged to an intermediate slab size in the noring teeming so as to obtain a carbo co t t approaehjng h mal manner, that is, care was taken so that the surface was not desired limit. It is significant to point out that heats 111(3577 unduly contaminated and there was Protection against interand HK35 78 did not h v a carbon dd d d yet were on granular oxidation. After forging to the intermediate slab size the upper end f the d i d range li i f h carbon the slabs were reheated and hot-rolled to an intermediate tent. band size within the range between 0.100 inch and 0.125 inch. The final carbon resulting from said air melting is set forth 1 5 The hot-rolled bands intermediate thickness e in Table II. These data clearly demonstrate the necessity for thoroattol' sootlohod. lohgltuohhahy and o of the band critically controlling the carbon content in order to control was shbleotod t ah lhtel'modloto ahhoahhg treatment and the the oxygen content in order to obtain the desired control of other was subleoted to a descahhg tl'oattheht h thoreafter oxygen so that beneficial results achieved by employing the oold'rohod o a finish gauge of 0014 lhohos thlohho5S process of the present invention. While all of the sulfur conwlthout lhtormedlato o h The other matenal tents were air melted to a chemistry below 0.005% it is noted after belhg sublectod to an lhtermedlato h treatment at a that there is a wide variation in the amount of oxygen and cartreatment at a temperature of about 1,000 for a b bon which is present within the materials as they have been hours was thorooftel' desoalod and oold'rohoo to a fihlsh melted. thickness of 0.014 inches without any further intermediate As stated previously the carbon content was adjusted during heat treatment- Matohals o o the directly f the teeming operation to produce the final carbon contents set thatohal as t matohal which had been Subjected to a forth hereinbefore Table II. Following the casting of the five hot band lhtol'mothate anneal were thereafter Subjected to 3 initial air melts into ingot form, the ingots were utilized as final heat treatment, P at a temperature of about 1 C electrodes and subjected to a vacuum arc furnace remelting and a P at about 1,2000 C! a time Period 0f4 hours wherein the electrode is consumed in the electric arc and ploying a hydrogen atmosphere of about "75 C. dew point. melted to form the final ingot. Such vacuum remelting is effec- Thereafter these materials were tested for their initial permeative for further carbon deoxidization of the alloy to which the yprocess of the present invention is applicable as can be seen Reference 15 directed to Table IV Whlch ta ulates the hereinafter in Table III. results of the measurement of the initial permeability for each TABLE IV Initial permeability Sulfur Carbon Hot band Final content content anneal anneal after 0 before after T. C.)/ '1. C.)/ .1 1 anneal anneal anneal Heat No. t. (hrs) t. (hrs) (60 Hz) (p.p.m.) (p.p.m.) (percent) HKV3575 None"... 1,150/4 9,860 6.0 s .0044 None"... 1,200/4 12,660 2.1 .0075 1,000/3o. 1,150/4 3,000 6.9 .0033 1,000 1,200 4 12.400 2.1 0065 HKV3575 N0ne 1,150/4 0,160 0.0 .0031 None 1,200/4 10,010 1.3 .0062 1010/30" 1,150/4 8,960 0.0 .0035

HKV3577 None. 1,150/4 10,010 5.9 .0075 None. 1, 200/4 15,130 0.8 4 .0060 1000/30.. 1,150 4 9,400 5.9 .0054 1,000/30... 1,200/4 15, 050 0.3 .0043

HKV3578 None-.. 1,150/4 10, 730 4.6 .0050 Norie 1,200/4 14,040 11 3 .0077 1,000 30... 1,150/4 0,120 4.6 .0041 1, 000/3 1, 200/4 15,040 1.1 .0065

HKV3579 None. 1,150/4 9, 700 8.2 .0032 None 1,200/4 10, 320 1.4 .0071 1,000/30. 1,150/4 0, 350 3.2 .0033 1,000/30 1,200 4 10,380 1.4 .0005

TABLE III of the materials together with the corresponding sulfur and vacuum m chemical analysis carbon contents as well as the hot-rolled band and final an- (In percent except where indicated) li h t nm d ta.

Ni Mn C O From Table IV it can be seen that higher final annealing g-gg fig 85? temperatures are effective for removing additional sulfur and 47:89 1 4 10014 consequently reduce the sulfur content to suitable low levels 78 3 below 5 ppm. Thus a direct correlation exists between the sul- 43.01 .73 .010 56 .0024

fur and oxygen content and the initial permeability that may luethyleng B0 ugtl W g K be attained in the material. While no correlation is apparen From the chemical analysis set forth in Table II] it becomes between the carbon content after final anneal and the apparent that a large reduction in the oxygen content has ocdeveloped initial permeability, nonetheless the carbon content curred. This deoxidation is believed to have occurred by the melt having been subjected to a vacuum environment so that as the carbon reacts with the oxygen, it thereby readily removes the same in the form of a gaseous carbon oxide most is related to the oxygen content, consequently it appears that a criteria for a suitable chemistry exists for the attainment of a high initial permeability. Thus when the initial permeability is selected for a minimum amount of 14,000 it becomes clear probably carbon monoxide. It may also be noted at this junc- 75 that the carbon content must be limited to about 75 ppm max,

the oxygen content to about ppm max, a sulfur content of about 2 ppm max, with the nickel, iron and manganese being within ordinary limits.

it has been noted however that even where the sulfur content is low and the carbon and oxygen content is low one other criteria is necessary in order to develop the high initial permeability. This criteria includes a coarse grain secondary recrystallized microstructure. Examination of the materials subjected to a final anneal which had not been given an intermediate anneal at their hot-rolled band size indicates that a coarse grain secondarily recrystallized structure is obtained. Where however the material is subjected to a hot band anneal, a coarse grain secondary recrystallized microstructure was not obtained in that such recrystallization was incomplete or the grain size of the secondarily recrystallized microstructure was exceedingly fine thereby inhibiting the development of the optimum initial permeability. Examination of the penultimate grain size indicated that a coarse grain structure was attained at the intermediate anneal. No amount of subsequent cold work was effective for producing a secondary recrystallized microstructure exhibiting a large or coarse grain size. Thus a comparison of the data indicates that if the oxygen and sulfur are low the optimum permeability is obtained with a coarse secondary recrystallized microstructure. Thus at 1,150 C. the annealed hot-rolled band material in all cases has undergone only a partial secondary recrystallization. Consequently where the proper carbon control is employed in the air melting then the necessity for hot-rolled band anneal can be eliminated thus resulting in a cost savings as well as the attendant advantage of improved magnetic characteristics. This becomes especially so when the results of heats HKV3577 and HKV3578 are compared with the balance of the heats. Heat HKV3577 indicates the possibility of obtaining an initial permeability of about 15,000 where the carbon and sulfur and oxygen contents are controlled and the material is subjected to a final heat treatment so as to produce a coarse secondary recrystallized microstructure. Annealing the hot-rolled band gauge at 1,000 C. for 30 hours produced a decided disadvantage even though the final sulfur content was reduced to a value of less than one part per million. Accordingly, the final criteria appears to be that the material must possess a coarse grain secondary recrystallized microstructure in order to obtain the high initial permeability.

I claim as my invention:

1. In the method of producing iron-nickel alloys having a high initial permeability, the steps comprising making an air melt of components to produce an alloy containing between about 47 and about 50% by weight of nickel, 0.60% to 1.0% manganese, less than about 0.005% sulfur and the balance essentially iron, decarburizing the melt to a value of less than about 0.035% by weight, casting the melt into ingot form while adjusting the carbon content to a value of between about 0.020% and 0.035%, vacuum arc remelting the cast ingot as an electrode to produce an ingot with an oxygen content of less than about 5 ppm of oxygen, hot working the remelted alloy to an intermediate gauge and cold working the material to finish gauge and heat treating the finish gauge alloy to reduce the carbon content to less than ppm, the oxygen content to less than 5 ppm, and the sulfur content to less than 2 ppm, and effecting a substantially complete secondary recrystallized microstructure.

2. The method of claim 1 in which the amount of carbon added during casting of the air melt is about 2% times the difference between the air melt analysis and 0.020 to 0.035%.

3. The method of claim 1 in which the heat treatment of the finish gauge material takes place at a temperature within the range between about 1, 1 50 and 1,200 C.

4. The method of claim 3 in which the material has a finish gauge thickness of less than about 0.014 inch and the anneal is conducted in an atmosphere of hydrogen having a dew point of less than 40 C.

5. In the method of producing Ni-Fe alloys having a high initial permeability the steps comprising making a air melt containing between about 47 and about 50% by weight of nickel, less than about 0.005% sulfur and the balance essentially iron with incidental impurities, the carbon content of said air melt to a value of less than about 0.035% by weight, casting the melt into ingot form while adjusting the carbon content to a value of about 0.025% by weight, remelting the cast ingot in a vacuum atmosphere to reduce the oxygen content to a value below 5 ppm, hot working the remelted ingot to an intermediate gauge within the range between about 0.100 and about 0.250 inch, cold working the material to finish gauge of not greater than about 0.014 inch without any intermediate heat treatment and thereafter subjecting the material of finish gauge to a heat treatment at a temperature within the range between about 1,l50 and 1,200 C. in hydrogen of a dew point of less than -40 C., to reduce the carbon content to less than 80 ppm, the oxygen content to less than 5 ppm, the sulfur content to less than 2 ppm and produce a coarse secondarily recrystallized microstructure.

6. The method of claim 5 in which the amount of carbon added during casting of the air melt is about 2% times the difference between the air melt analysis and 0.025%.

7. A cold rolled and annealed member of an alloy having a high initial permeability of above 10,000 in a field of 40 gauss at 60 Hz, the alloy consisting essentially of from 47 to 50% by weight of nickel, from 0.6 to 1.0% by weight of manganese, less than 0.005% sulfur, carbon less than about 0.008%, less than 5 ppm of oxygen, the alloy-being secondarily recrystallized and having a coarse grain structure with the majority of the volume comprising grains of an average diameter in excess of 0.25 inch, and produced by the method of claim 1. 

2. The method of claim 1 in which the amount of carbon added during casting of the air melt is about 2 1/2 times the difference between the air melt analysis and 0.020 to 0.035%.
 3. The method of claim 1 in which the heat treatment of the finish gauge material takes place at a temperature within the range between about 1,150* and 1,200* C.
 4. The method of claim 3 in which the material has a finish gauge thickness of less than about 0.014 inch and the anneal is conducted in an atmosphere of hydrogen having a dew point of less than 40* C.
 5. In the method of producing Ni-Fe alloys having a high initial permeability the steps comprising making a air melt containing between about 47 and about 50% by weight of nickel, less than about 0.005% sulfur and the balance essentially iron with incidental impurities, the carbon content of said air melt to a value of less than about 0.035% by weight, casting the melt into ingot form while adjusting the carbon content to a value of about 0.025% by weight, remelting the cast ingot in a vacuum atmosphere to reduce the oxygen content to a value below 5 ppm, hot working the remelted ingot to an intermediate gauge within the range between about 0.100 and about 0.250 inch, cold working the material to finish gauge of not greater than about 0.014 inch without any intermediate heat treatment and thereafter subjecting the material of finish gauge to a heat treatment at a temperature within the range between about 1,150* and 1,200* C. in hydrogen of a dew point of less than -40* C., to reduce the carbon content to less than 80 ppm, the oxygen content to less than 5 ppm, the sulfur content to less than 2 ppm and produce a coarse secondarily recrystallized microstructure.
 6. The method of claim 5 in which the amount of carbon added during casting of the air melt is about 2 1/2 times the difference between the air melt analysis and 0.025%.
 7. A cold rolled and annealed member of an alloy having a high initial permeability of above 10,000 in a field of 40 gauss at 60 Hz, the alloy consisting essentially of from 47 to 50% by weight of nickel, from 0.6 to 1.0% by weight of manganese, less than 0.005% sulfur, carbon less than about 0.008%, less than 5 ppm of oxygen, the alloy being secondarily recrystallized and having a coarse grain structure with the majority of the volume comprising grains of an average diameter in excess of 0.25 inch, and produced by the method of claim
 1. 